Lot of good ones mentioned. We had a fun football game for 3 ppl where one would be qb and the other two would go out for a pass. Both were on offense but as soon as one caught the ball the other one became defense. We spent a lot of time with me as the qb throwing a lot of passes to my friends little brother so my friend could blow him up on the tackle.
Also I had a one person baseball game where I pitched a tennis ball against the front steps and then tried to catch the ball for an out. If I missed, then it depended on where the ball landed on if it was a single, double, triple or home run.
One of my favorite things not mentioned so far was crawdad hunting in the creek. We used to do that all summer long.
We had a 3 person football game as well. A qb, wr, and db. A TD pass was worth 6 pts for qb and wr. A def stop was worth 4 pts and a pick was worth two (plus 4 for the stop equaling 6). A pick-6 was worth 12. You had four downs to score.
After the series, everyone rotated. QB went to DB, DB to WR, and WR to QB. First one to 30 points (usually) won. This was a decent game because we could play it in the street under the street light at night.